Hope for portable MRI scanners

CHEAP, hand-held MRI scanners could one day replace the cumbersome and expensive machines now used in hospitals to create three-dimensional maps of body tissue. The breakthrough is promised by the development of an atomic magnetometer, which can pick up extremely weak magnetic signals.

To generate an image, a conventional MRI scanner applies a strong magnetic field that initially aligns the spins of hydrogen nuclei within the body's water molecules. Zapping the patient with short bursts of radio waves knocks these spins out of alignment, and as they get back into line they wobble or "precess" like spinning tops. This generates an oscillating magnetic field that can be picked up by a magnetic sensor and used to map the tissues.

But these oscillating fields are weak, and to ensure that they are at least strong enough to be picked up by the detectors used in conventional MRI machines the applied magnetic ...

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